The present invention relates to a retractable and destructible safety syringe which has a simple structure and which can be easily manufactured at low cost and commercialized.
Various types of disposable syringes are currently widely used. After being discarded, large amounts of such syringes result in pollution problems. The used syringes often injure medical personnel and infect the personnel with viruses or bacteria carried by patients who have earlier used the syringes. In particular, a serious danger presented to medical personnel and others handing used syringes is exposure to the AIDS virus.
In order to solve the above-mentioned problems, various types of retractable syringes have been developed. For example, in one syringe type, a spring is installed between the syringe barrel and the piston for pulling the needle back into the barrel after injection. However, due to the properties of the medications held within the syringe barrel and as a result of safety requirements, the materials which may be used to manufacture the spring are strictly limited. Therefore, the structure of such a syringe is complicated and the manufacturing cost is very high. Various types of safety syringes free from the springs just described have been also developed. In such syringes, a latch member is disposed at the bottom of the syringe barrel, whereby when the plunger is pushed to the bottom of the barrel, the latch member latches the plunger to the needle. Then, when the plunger is pulled back, the needle is retracted into the barrel along with the plunger so as to avoid risk of injury from the needle to medical personnel and others handling the syringe.
In order to avoid leakage of the liquid medicine within the syringe and to avoid unexpected disconnection of the needle from the barrel, the needle must be firmly attached to the barrel. However, if the needle is too firmly attached to the barrel, it will be difficult to pull the needle back into the barrel. Therefore, the manner in which the needle is attached to the syringe barrel presents a challenging design problem.
In addition, in the case where it is necessary to securely latch the plunger with the needle, firm engagement required for secure latching presents another design difficulty. Conversely, designs in which the plunger and needle easily latch together often provide unreliable engagement, resulting in latching which is insufficient to pull the needle back into the barrel. Therefore, a reliable assembly to latch the plunger with the needle also presents a challenging design problem.
Moreover, in conventional syringe designs employing a retractable needle as described above, it often occurs that before the injection is completed, the plunger is latched with the needle by mistake. This leads to waste of the needle and syringe.